1. Field of the Invention
The present invention relates to a liquid crystal display LCD and, particularly to a color filter substrate for a liquid crystal display such that, not only an indium tin oxide ITO pattern terminal is also formed at the same time when a black matrix is formed by the use of chromium, improving the adhesive strength of the ITO transparent electrode but also a tape automated bonding drive integrated circuit TAB drive IC can be advantageously distinguished at a following process step of mounting it, making the automation of process possible and improving the productivity.
2. Description of the Art
Recently, according as the spread of an office automated machine or a potable small size television, studies on liquid crystal display LCD, electroluminescence EL element, plasma display panel PDP, light emitting diode LED, vacuum fluorescent display VED and the like have vigorously carried out and a part of them is under utilization.
Among them, the LCD has a thin thickness, a low weight and is low in price. This display has a good match for the integrated circuit, driven by the less consumption of voltage. So, the liquid crystal display has been widely used as an alternative to cathode ray tubes in display monitors for vehicles or in a screen of color televisions as well as in display monitors for lap top personal computers or pocket computers.
Also, as a color filter used in the LCD, 3-5 inch has been in practice. 10-14 inch is under development. Further color filter size is on the rapid trend of enlargement.
Like a color cathode ray tube CRT, a color filter is a technology of realizing colors such that a base unit of picture element consists of three primary colors of the light and the intensity of the three colors is modulated, namely the intensity of the passing light being modulated.
The color characteristic is most advantageous in the active matrix liquid crystal panel having the contrast ratio of 40:1. However, compared with the manufacture of a monochro liquid crystal, the manufacture of the color liquid crystal has disadvantages of the increased picture elements (three times), the increased marginal integrated circuits (driver etc), the cost increase and the low yield.
As a conventional method of forming the color filter layer, there are a printing method, a depositing method, an electrodeposition method, a pigment scattering method and the like. Generally, the printing method is used. This method is divided into two types: a positive type and a negative type according to a method of using a resist. In a dyeing layer is used a natural turu-back material such as a gelatin, casein and the like. The gelatin is easily advantageously dyed.
Also, in the LCD technology, the uniformity of the distance between cell gaps is most important. To obtain the uniformity, the surface of the color filter layer is to be formed in the flatness. The good processing technology for this flatness is to be needed.
In the process for dyeing the color filter layer, there are a mask method and a pattern method. The pattern method has a excellent smoothening quality, resulting in an advantageous utilization. When using a positive resist, there follows an unstable isolation.
This LCD is formed by a lower substrate having a thin film transistor TFT of individual switching element, namely a TFT substrate; a upper substrate having the color filter layer, namely a color filter substrate; and a liquid crystal sealed in the small space formed between the upper and lower substrates.
The manufacturing method of a conventional color filter having the color filer layer will be described as follows.
After cutting, polishing and annealing the upper glass substrate 1, chromium is applied to a thickness of 1000 to 2000 angstroms and patterned to define a plurality of cells. A plurality of black matrixes 2 for blocking light are thereby formed on the upper glass substrate to prevent degradation of thin film transistors.
A material in which pigment is scattered to optimize red spectroscopic characteristics, e.g., a colored acrylic photosensitive resin layer, is applied on the surface of the upper glass substrate with black matrix. It is soft-baked in a hot plate, and then exposed to ultraviolet rays. The colored acrylic photosensitive resin layer is developed by a developer for two to three minutes, and then rinsed by deionized water for 90 second, thereby forming a first color filter layer 3 with optimized red spectroscopic characteristics.
In the same manner as the first color filter layer, a second color filter layer of a colored acrylic photosensitive resin layer having optimized green spectroscopic characteristic is formed on the upper glass substrate, separated from the first color filter layer.
Subsequently, a third color filter layer 5 of a colored acrylic photosensitive resin layer having optimized blue spectroscopic characteristics is formed on the upper glass substrate, separated from the second color filter layer.
In order to protect the black matrix and color filter layers from external impact, a transparent resin layer made of polyimide, polyacrylate, or polyurethane having high surface solidity and excellent photo-transmittivity is formed to a thickness of 0.5 .mu.m-3 .mu.m, then soft-baked for five minutes in a hot plate between 150.degree. C.-220.degree. C., thereby forming a protective film 6. The formation of the upper substrate is completed by forming a transparent electrode layer 7 of indium tin oxide, to which voltage for liquid crystal driving is applied, on the protective film to a thickness of 500-1300 angstroms.
In the meantime, the color filter layer comprises the black matrix formed on the upper glass substrate I for preventing degradation of the transistor; a plurality of color filter layers having red, green and blue dyes 3, 4 and 5 sequentially interspersed among the black matrix 2; the protective film 6 formed on the black matrix 2 and the color filter layer 3, 4 and 5;and the transparent electrode layer of ITO formed on the protective film.
In the color filter of the above method, the ITO is deposited on the transparent electrode at a low temperature, so that, at the time of repairing the ITO layer, ITO lines are easily cut off even by slight scratch, resulting in high poor productivity. Also, the low density of the ITO causes the resistance and the adhesive strength to the other deposited materials, for example, protective films of resin to be low and bad, resulting in a broken film and a line short. In addition, the ITO electrode is not well distinguished by human eyes or a charge coupled device CCD camera, so that it is difficult to mount the element exactly at the following step of a tape automated bonding drive integrated circuit.